1. Technical Field
The present disclosure relates to a waveguide device and a slot antenna.
2. Description of the Related Art
Examples of waveguiding structures which include artificial magnetic conductors are disclosed in Patent Documents 1 to 3, and Non-Patent Documents 1 and 2.
An artificial magnetic conductor is a structure which artificially realizes the properties of a perfect magnetic conductor (PMC), which does not exist in nature. One property of a perfect magnetic conductor is that “a magnetic field on its surface has zero tangential component”. This property is the opposite of the property of a perfect electric conductor (PEC), i.e., “an electric field on its surface has zero tangential component”. Although no perfect magnetic conductor exists in nature, it can be embodied by an artificial structure, e.g., an array of a plurality of electrically conductive rods. An artificial magnetic conductor functions as a perfect magnetic conductor in a specific frequency band which is defined by its structure. An artificial magnetic conductor restrains or prevents an electromagnetic wave of any frequency that is contained in the specific frequency band (propagation-restricted band) from propagating along the surface of the artificial magnetic conductor. For this reason, the surface of an artificial magnetic conductor may be referred to as a high impedance surface.
In the waveguide devices disclosed in Patent Documents 1 and 2 and Non-Patent Documents 1 and 2, an artificial magnetic conductor is realized by a plurality of electrically conductive rods which are arrayed along row and column directions. Such rods are projections which may also be referred to as posts or pins. Each such waveguide device, as a whole, includes a pair of opposing electrically conductive plates. One conductive plate has a ridge protruding toward the other conductive plate, and stretches of an artificial magnetic conductor extending on both sides of the ridge. An upper face (i.e., its electrically conductive face) of the ridge opposes, via a gap, a conductive surface of the other conductive plate. An electromagnetic wave (signal wave) of a wavelength or frequency which is contained in the propagation-restricted band of the artificial magnetic conductor propagates along the ridge, in the space (gap) between this conductive surface and the upper face of the ridge.    [Patent Document 1] International Publication No. 2010/050122    [Patent Document 2] the specification of U.S. Pat. No. 8,803,638    [Patent Document 3] European Patent Application Publication No. 1331688    [Non-Patent Document 1] Kirino et al., “A 76 GHz Multi-Layered Phased Array Antenna Using a Non-Metal Contact Metamaterial Waveguide”, IEEE Transaction on Antennas and Propagation, Vol. 60, No. 2, February 2012, pp 840-853    [Non-Patent Document 2] Kildal et al., “Local Metamaterial-Based Waveguides in Gaps Between Parallel Metal Plates”, IEEE Antennas and Wireless Propagation Letters, Vol. 8, 2009, pp 84-87    [Non-Patent Document 3] Tomas Sehm et al., “A High-Gain 58-GHz Box-Horn Array Antenna with Suppressed Grating Lobes”, IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 47, NO. 7, JULY 1999, pp 1125-1130.